Identification of virulent pathotypes causing rice blast disease (Magnaporthe oryzae) and study on single nuclear gene inheritance of blast resistance in F2 population derived from pongsu seribu 2 × mahshuri

Ten pathotypes of Magnaporthe oryzae found in Malaysia were tested against thirteen different Malaysian modern rice varieties/cultivars including resistant and susceptible to identify the most virulent pathotypes. The inheritance of blast disease resistance was studied using local cultivars by making normal and reciprocal crosses between resistance variety Pongsu Seribu 2 (Oryza sativa L. subsp. indica) and susceptible variety Mahsuri (Oryza sativa L. subsp. indica). Pathotype pathotype P7.2 followed by pathotype P5.0 was found as the most virulent against the cultivars. The disease scale of >2.5 was observed in six varieties against P7.2 and in five varieties against pathotype P5.0. Nineteen F1 hybrids were confirmed using SSR marker RM168 and were selfed to produce F2 populations. A total of 2560 F2 plants from normal crosses and 3182 from reciprocal crosses were challenged with pathotype P7.2. A 3:1 (R:S) segregation ratio was observed in both types of crosses using the chi-square test, indicating the maternal effect which showed resistance to the blast disease caused by pathotype P7.2 is most likely controlled by a single nuclear gene. As a single resistance gene is able to retain the resistance for a short period, developing new breeding lines will be the alternative, rather than having no resistant material with multiple genes.